Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

There is disclosed an antenna arrangement comprising an electrically
conductive radiating element having first and second ends, an
electrically conductive ground plane or ground member, and an input
terminal. The radiating element has a plurality of separate feed points
at different locations between its first and second ends, and the input
terminal is provided with a switch. Each feed point is electrically
connected to the switch by way of a separate electrical pathway, the
switch being configured to allow the separate feed points to be
connected individually or in predetermined combinations to the input
terminal by selecting between a plurality of selectable contacts. At
least one of the electrical pathways includes a capacitive circuit
component connected in series, and at least one other of the electrical
pathways includes an inductive circuit component connected in series. The
antenna arrangement allows for a high degree of customization and
improved matching, and enables good multi-band performance.

Claims:

1. An antenna arrangement comprising an electrically conductive radiating
element having first and second ends, an electrically conductive
groundplane, and an input terminal; wherein the radiating element has a
plurality of separate feed points at different locations between its
first and second ends, wherein the input terminal is provided with a
switch, and wherein each feed point is electrically connected to the
switch by way of a separate electrical pathway, the switch being
configured to allow the separate feed points to be connected individually
or in predetermined combinations to the input terminal by selecting
between a plurality of selectable contacts, and wherein at least one of
the electrical pathways includes a capacitive circuit component connected
in series and wherein at least one other of the electrical pathways
includes an inductive circuit component connected in series.

2. An arrangement as claimed in claim 1, wherein there are two feed
points.

3. An arrangement as claimed in claim 1, wherein there are at least three
feed points.

4. The arrangement of claim 1, wherein a first end of the radiating
element is electrically connected to the groundplane.

5. The arrangement as claimed in of claim 4, wherein the connected to the
groundplane is by way of a capacitive and/or inductive circuit component.

6. The arrangement of claim 1, wherein at least one resistive circuit
component is connected in series with the radiating element between at
least one pair of feed points.

7. The arrangement of claim 1, wherein at least one inductive circuit
component is connected in series with the radiating element between at
least one pair of feed points.

8. The arrangement of claim 1, wherein at least one capacitive circuit
component is connected in series with the radiating element between at
least one pair of feed points.

9. The arrangement of claim 1, wherein matching networks comprising
inductive and/or capacitive circuit components are connected in series
with the electrical pathways.

10. The arrangement of claim 9, wherein the matching networks include at
least some circuit components connected to the groundplane.

11. The arrangement of claim 1, wherein the radiating element takes the
form of a loop antenna comprising a dielectric substrate having first and
second opposed surfaces and a conductive track formed on the substrate,
wherein there is provided a first feed point, a second feed point and a
grounding point on the first surface of the substrate, with the
conductive track extending from the first feed point and the grounding
point respectively, then extending towards an edge of the dielectric
substrate, then passing to the second surface of the dielectric substrate
and then passing across the second surface of the dielectric substrate
along a path generally following the path taken on the first surface of
the dielectric substrate, before connecting at a conductive loading plate
formed on the second surface of the dielectric substrate that extends
into a central part of a loop formed by the conductive track on the
second surface of the dielectric substrate.

12. The arrangement of claim 11, wherein the first feed point is
configured as an inductive feed and the second feed point is configured
as a capacitive feed.

13. (canceled)

Description:

[0002] The growth of mobile radio applications has led to the development
of services using a variety of different air interface standards and
radio frequency bands in different parts of the world. A current
generation mobile phone is likely to provide for transmissions using the
GSM or UMTS air interfaces (as defined by the international standards
body 3GPP) on the 850 MHz, 900 MHz, 1800 MHz, 1900 MHz and 2100 MHz
frequency bands. The development of compact antennas capable of operating
on all these bands, for use in mobile handsets, laptop computers,
trackers and other user equipment (UE) is very challenging. The
development of antenna techniques has in general been evolutionary,
simple dual band structures being progressively optimized to provide
wider operating bandwidths at each of the two frequency bands. Current
`pentaband` antennas operate over the frequency bands 826-960 MHz and
1710-2170 MHz.

[0003] The economics of handset design and production, as well as users'
requirements for world-wide roaming, imply that a handset is required to
operate on all the standard frequency bands associated with the interface
protocol(s) which it supports.

[0004] The advent of new mobile services in the frequency band 698-798
MHz, when combined with existing requirements in the band 826-960 MHz
creates a new challenge to the antenna designer. The present invention
provides a means by which this requirement may be satisfied without any
significant increase in the volume occupied by the antenna.

[0005] With reference to FIG. 1, it is well known that a single radiating
element 10 may be fed concurrently with radio signals at two frequencies,
f1 and f2 by the means shown in FIG. 1, where 11 is a band-stop filter
tuned to f2, 12 is a band-stop filter tuned to f1, 13 is an input
matching circuit adjusted to provide the required matched input impedance
at f1 and 14 is an input matching circuit adjusted to provide the
required matched input impedance at f2. Such an arrangement works well if
the bandwidths of the signals at f1 and f2 are small compared with their
frequency separation (f1-f2). If the frequency separation is small or the
bandwidth is large, then the design of suitable filters and matching
circuits becomes difficult--their cost, dimensions and associated
transmission losses become unacceptably large.

[0006] Alternative arrangements providing for optional transmission at f1
or f2 may be designed as shown in FIG. 2 by making use of a switch 15 at
the antenna input and two alternative matching circuits, one for f1 [13]
and the other for f2 [14]. Such an arrangement is satisfactory in many
circumstances, but presupposes that the antenna may be matched
effectively and economically for both frequency bands f1 and f2 when the
feed point to the antenna is at one fixed location.

[0007] In the case of mobile radio antennas, the large width of the
frequency bands in which f1 and f2 may be positioned, the small
fractional separation between the adjacent ends of these frequency bands,
and the necessarily small physical dimensions of the antenna (typically
0.2×0.06×0.025 wavelengths) result in an input impedance
which is very difficult to match effectively over the specified bands.
The result of inadequate impedance matching is reduced antenna efficiency
with consequential reduced range, data rate and battery life.

BRIEF SUMMARY OF THE DISCLOSURE

[0008] According to a first aspect of the present invention, there is
provided an antenna arrangement comprising an electrically conductive
radiating element having first and second ends, an electrically
conductive groundplane or ground member, and an input terminal; wherein
the radiating element has a plurality of separate feed points at
different locations between its first and second ends, wherein the input
terminal is provided with a switch, and wherein each feed point is
electrically connected to the switch by way of a separate electrical
pathway, the switch being configured to allow the separate feed points to
be connected individually or in predetermined combinations to the input
terminal by selecting between a plurality of selectable contacts, and
wherein at least one of the electrical pathways includes a capacitive
circuit component connected in series and wherein at least one other of
the electrical pathways includes an inductive circuit component connected
in series.

[0009] For example, where two feed points are provided, spaced from each
other along the radiating element, there will be two electrical pathways
connecting the switch to the radiating element, one for each feed point,
and the switch will be configured to allow one or other of the two
electrical pathways to be connected to the input terminal. One of the
pathways will include a capacitive circuit component connected in series
between the input terminal/switch and the feed point associated with that
pathway, while the other pathway will include an inductive circuit
component connected in series between the input terminal/switch and the
feed point associated with the other pathway. Where three feed points are
provided, there will be three electrical pathways and the switch will be
operable selectively to connect any one of the three electrical pathways
to the input terminal. Any number of feed points and associated pathways
and selectable contacts may be provided for particular applications,
provided that the number is always two or more, and provided that at
least one pathway includes a capacitive circuit component and at least
one other pathway includes an inductive circuit component.

[0010] It has been found that a spacing between the feed points along the
radiating element is an important parameter, and must be carefully
selected in order to achieve good antenna operation. The feed impedance
changes as a function of position along the radiating element. The choice
of feed position therefore depends on the configuration of the radiating
element and the frequencies that are of interest.

[0011] In simpler embodiments, each feed point and associated pathway is
individually switched in by the switch--that is to say, when one feed
point and pathway is switched in, all of the others are switched out.
However, in more complex embodiments, two or more feed points and
associated pathways may be connected at the same time to the input
terminal. This provides additional degrees of freedom and to provide a
wider bandwidth in some applications.

[0012] Each pathway and feed point may be associated with a predetermined
frequency band.

[0013] In some embodiments, the radiating element, or at least one end
thereof, is electrically connected to the groundplane or ground member,
either directly (galvanically) or through an inductive and/or capacitive
circuit component. This provides an additional degree of freedom which
can help match the antenna in particular circumstances.

[0014] In some embodiments, resistive, inductive and/or capacitive circuit
components may be placed in series with the radiating element between the
feed points. Where there are three or more feed points, different circuit
components may be placed in series between different pairs of feed
points, or circuit components may be placed between some pairs of feed
points and not others. For example, where there is a large difference
between two required operating frequency bands, it has been found that
placing an inductor in series with the radiating element, between two
feed points, can facilitate matching at both bands.

[0015] In a further embodiment of the invention, matching networks
comprising inductive and/or capacitive circuit elements may optionally be
connected in series with the feeding pathways. Such tuning elements may
optionally contain circuit elements connected to ground, but any
impedance to ground will cause a change in the impedances presented at
all feed points and not only the feed point at which the element is
positioned; by contrast, circuit elements connected in series will change
the input impedance at the associated switch input terminal while having
little effect on the impedance presented at other input terminals.

[0016] It will be appreciated that in any single embodiment the inductive,
capacitive and/or circuit elements may each be optionally provided or
omitted, the place of omitted elements being taken by a direct connection
(a nominal impedance of 0+j0 ohms), provided always that there is one
feed point connected to the input terminal/switch by way of a pathway
with an inductive circuit component connected in series, and another feed
point connected to the input terminal/switch by way of a pathway with a
capacitive circuit component connected in series.

[0017] In a particularly preferred embodiment, the radiating element takes
the form of a loop antenna comprising a dielectric substrate having first
and second opposed surfaces and a conductive track formed on the
substrate, wherein there is provided a first feed point, a second feed
point and a grounding point on the first surface of the substrate, with
the conductive track extending from the first feed point and the
grounding point respectively, then extending towards an edge of the
dielectric substrate, then passing to the second surface of the
dielectric substrate and then passing across the second surface of the
dielectric substrate along a path generally following the path taken on
the first surface of the dielectric substrate, before connecting at a
conductive loading plate formed on the second surface of the dielectric
substrate that extends into a central part of a loop formed by the
conductive track on the second surface of the dielectric substrate.

[0018] The first feed point is configured as an inductive feed, for
example an inductively-coupled loop or a galvanic tap connection, and the
second feed point is configured as a capacitive feed.

[0019] It will be appreciated that while the foregoing is framed in terms
of the antenna arrangement acting as a transmitter, the discussion
applies equally to the antenna arrangement when operating in receiver
mode. Indeed, all antennas generally work both to transmit and to receive
Radio Frequency (RF) signals, one being the reciprocal equivalent of the
other, and it is standard practice when describing antennas to do so in
terms of their transmitting characteristics, the receiving
characteristics being implied and derivable from the transmitting
characteristics. Accordingly, embodiments of the present invention apply
both to transmitting as well as receiving configurations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For a better understanding of the present invention and to show how
it may be carried into effect, reference shall now be made by way of
example to the accompanying drawings, in which:

[0021]FIG. 1 shows a prior art antenna arrangement in which a single
radiating element is fed with two signals at different frequencies;

[0022]FIG. 2 shows an alternative prior art antenna arrangement in which
a single radiating element is fed with two signals at different
frequencies;

[0023]FIG. 3 shows in schematic form a first embodiment of the present
invention, in which an antenna radiating element is fed at two separate
feed points;

[0024]FIG. 4 shows in schematic form a second embodiment of the present
invention, in which additional capacitive and/or inductive components are
incorporated;

[0026]FIG. 7 is a plot of the measured return loss of the embodiment of
FIGS. 5 and 6 for the 698-798 MHz band;

[0027]FIG. 8 is a plot of the measured return loss of the embodiment of
FIGS. 5 and 6 between 800 MHz and 2500 MHz; and

[0028] FIG. 9 compares three feed arrangements.

DETAILED DESCRIPTION

[0029] An improved arrangement is shown in its simplest form in FIG. 3 in
which there is provided a conductive antenna member 20 acting in
conjunction with a grounded member 11. The end 21 of the conductive
antenna member 20 may optionally be connected to the grounded member 11.
At least two separate feed points 22, 23 are provided on the antenna
member and are connected by a corresponding number of conductors 24, 25
respectively to the input terminal 27 by means of an input switch 26
having the same number of selectable contacts as the number of feed
points and connecting conductors which allows the selection of the feed
system associated with each frequency band.

[0030] A capacitive circuit component 29 is connected in series in the
pathway defined by the conductor 25, and an inductive circuit component
28 is connected in series in the pathway defined by the conductor 24.

[0031] In a further embodiment the end 21 of the antenna conductive member
20 is connected to the groundplane 11 directly or through an inductive or
capacitive circuit element 30 (as shown, for example, in FIG. 4).

[0032] Advantageously, as shown in FIG. 4, capacitive, inductive or
resistive circuit elements are optionally placed in series with the
antenna member between the feed points 22, 23.

[0033] In a further embodiment of the invention, matching networks
comprising inductive or capacitive circuit elements are optionally
connected in series with the feeding conductors. Such tuning elements may
optionally contain circuit elements connected to ground, but any
impedance to ground will cause a change in the impedances presented at
all feed points and not only the feed point at which the element is
positioned; by contrast, circuit element connected in series will change
the input impedance at the associated switch input terminal while having
little effect on the impedance presented at other input terminals.

[0034] In a preferred embodiment the conductive radiating element is
formed into a folded loop as described in UK patent application no
0912368.8 filed on 28 Jul. 2009 and illustrated in FIGS. 5 and 6. Here a
laminar dielectric member 49 supports a laminar ground conductor 11 and a
dielectric antenna support 42. The ends 43, 44 of the conductive
radiating member 41 terminate on the ground conductor 11. In this
exemplary embodiment two input connections 45, 46 are provided. The
connection at 45 is a galvanic connection made through a small coupling
loop 45-47-43, which may alternatively be described as a tap on the input
connection of the loop 41. The current in the loop 45-43-47 creates a
magnetic flux which couples via mutual inductance to the radiating member
41. It is to be appreciated that although the connection at 45 is, in the
illustrated embodiment, a directly tapped galvanic connection,
alternative embodiments do not require the inductive loop 45-43-47 to be
in galvanic contact with the radiating member 41. The second input
connection 46 is connected to the radiating element 41 via a capacitance
which is created between the input probe 47 and a portion of the
radiating element 48. The dimensions of the conductors 47 and 48 are
chosen to optimize the input impedance presented at the connection points
45 and 46. In an exemplary practical embodiment of the invention the
overall dimensions of the folded loop antenna are 50 mm×10
mm×3 mm. Input 45 provides for operation in the frequency band
698-798 MHz, while input 46 provides for operation in the frequency bands
826-890 MHz, 880-960 MHz, 1710-1880 MHz, 1850-1990 MHz and 1990-2170 MHz,
encompassing international assignments for three major mobile radio
protocols. FIG. 6 shows the underside of the laminar dielectric member 49
in the region of the dielectric antenna support 42. Capacitive connection
46 passes under the dielectric member 49 and couples capacitively with
the conductor 48 on the topside of the dielectric member 49.

[0035] The large number of degrees of freedom provided by embodiments of
the present invention enables the characteristics of an antenna to be
varied over a very wide range and enable the multiband operation
necessary in modern mobile radio devices.

[0036]FIG. 7 shows the measured return loss of the embodiment of FIG. 5
at the input port for the 698-798 MHz band. FIG. 8 shows the measured
return loss between around 800 MHz and 2500 MHz, showing that the antenna
arrangement works effectively also in the 850 MHz, 900 MHz, 1800 MHz,
1900 MHz and 2100 MHz bands. In FIG. 8, the indicated points are as
follows: 1) 824 MHz, 2) 960 MHz, 3) 1710 MHz and 4) 2170 MHz.

[0037] FIG. 9 shows, for illustrative purposes, a direct feed arrangement
contrasted with inductive and capacitive feeds as used in embodiments of
the present invention. In a direct feed (FIG. 9a), there is a direct
electrical connection from input terminal 90 to a radiating element 91 by
way of a conductive electrical pathway 92 connected to the radiating
element at feed point 93. In this embodiment, one end of the radiating
element 91 is connected to RF ground 94. FIG. 9b shows an inductive feed
arrangement, where a loop 95 is formed in electrical pathway 92', and
magnetic flux generated by the loop 95 couples inductively with the
radiating element 91 at feed point 93'. One end of the electrical pathway
92' is connected to RF ground 94 in this embodiment. FIG. 9c shows a
capacitive feed arrangement, where an electrical pathway 92'' extends
from the input terminal 90 and couples capacitively with the radiating
element 91 at feed point 93''.

[0038] Throughout the description and claims of this specification, the
words "comprise" and "contain" and variations of them mean "including but
not limited to", and they are not intended to (and do not) exclude other
moieties, additives, components, integers or steps. Throughout the
description and claims of this specification, the singular encompasses
the plural unless the context otherwise requires. In particular, where
the indefinite article is used, the specification is to be understood as
contemplating plurality as well as singularity, unless the context
requires otherwise.

[0039] Features, integers, characteristics, compounds, chemical moieties
or groups described in conjunction with a particular aspect, embodiment
or example of the invention are to be understood to be applicable to any
other aspect, embodiment or example described herein unless incompatible
therewith. All of the features disclosed in this specification (including
any accompanying claims, abstract and drawings), and/or all of the steps
of any method or process so disclosed, may be combined in any
combination, except combinations where at least some of such features
and/or steps are mutually exclusive. The invention is not restricted to
the details of any foregoing embodiments. The invention extends to any
novel one, or any novel combination, of the features disclosed in this
specification (including any accompanying claims, abstract and drawings),
or to any novel one, or any novel combination, of the steps of any method
or process so disclosed.

[0040] The reader's attention is directed to all papers and documents
which are filed concurrently with or previous to this specification in
connection with this application and which are open to public inspection
with this specification, and the contents of all such papers and
documents are incorporated herein by reference.